Preparation of nitro compounds by vapor phase nitration of ketones

ABSTRACT

A process for selectively forming nitro compounds by contacting, at elevated temperature and pressure and in a homogeneous gas phase, a ketone having from three to ten carbon atoms with nitrogen dioxide alone or in the presence of oxygen and/or water.

This application is a continuation-in-part application of copending U.S.application Ser. No. 510,860, Filed July 5, 1983, now abandoned.

BACKGROUND OF THE INVENTION

The present invention is directed to a process of forming anitroparaffin and nitroaromatic compounds by gaseous phase reaction of aketone with nitrogen dioxide. The present process provides a method toform pre-selected nitro compounds based on the particular ketone feed.The process further alleviates certain processing steps required in thepreviously used nitration of hydrocarbon feed such as ethane, propaneand the like.

Processes to form nitroparaffins by gaseous phase nitration are known.U.S. Pat. Nos. 3,780,115 and 3,869,253 teach that nitration of saturatedhydrocarbons higher than methane can be accomplished by contacting thehydrocarbon feed with nitrogen dioxide in the presence of oxygen, suchas in the form of air. The reactant gases are preheated and thenintroduced into the reaction zone where the gaseous phase nitration iscarried out at elevated pressure and at elevated temperature. Thegaseous effluent emitted from the nitration reaction zone is rapidlyquenched. The quenched mixture then enters a separator where the gaseousmaterials in the form of unreacted hydrocarbon, nitric oxide, carbonmonoxide and carbon dioxide are removed for subsequent purification andrecycling and the remaining phase liquid materials are separated bydecantation and the nitroparaffins are recovered by distillation. Thisnitration process yields a mixture of products having a predominance ofnitropropane and nitroethane.

French Publication No. 78/32,118 discloses that the nitroparaffinsproduct mixture can be made to have an increased yield of nitromethane,the most commercially desired product, by utilizing ethane as thehydrocarbon feed in the homogeneous gas phase nitration. The nitrationprocess can be further enhanced by recycling into the hydrocarbon feedsome of the nitropropane product and/or by conducting the nitration inthe presence of an inert gas such as nitrogen, hydrogen or argon.

U.S. Pat. No. 4,260,838, similar to the above French reference, teachesthat the gas phase nitration process of U.S. Pat. Nos. 3,780,115 and3,869,253 can be improved by altering the feed stock to obtain suitablepercentages of different nitroparaffins as suits the needs of themarketplace. This patent teaches that the feed stock be made up of amixture containing propane, preferably recycled nitroparaffin andpossibly inert gas and/or another alkane. The nitrating agent can beeither nitrogen dioxide or nitric acid.

Each of the conventional processes, such as those in the abovereferenced patents, relies on the use of a hydrocarbon feed whichprovides a nitroparaffin product mixture. These processes have thefurther defect of providing low yield of nitroparaffin mixture and lowselectivity of the most commercially desired compound, nitromethane.Finally, because of the low yield, processes which are based on thegaseous phase nitration of saturated hydrocarbons produce a large volumeof gaseous reaction effluents composed predominantly of unreactedhydrocarbon. In order to enhance these prior art processes, theunreacted hydrocarbons must be separated and recovered from theremaining gases, such as by cryogenic means, and then recycled as partof the process feed. Such separation and recovery required additionalequipment and adds to the processing costs of the known processes.

A method to selectively form particular nitroalkanes or nitroaromaticsfrom easily available and processable feed is highly desired. It isparticularly desired to have a process to selectively form nitromethane,a very industrially useful product.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a process by which aselective nitroparaffin can be formed or that a selective nitro compoundis the predominant compound of the resultant products.

Another object of the present invention is to provide a process by whichthe various unreacted feed materials are readily separated andrecyclable.

Another object of the present invention is to provide a process by whichone can selectively form nitromethane from readily available andprocessable materials.

The process of the present invention is capable of selectively formingparticular nitrohydrocarbon compounds by contacting in a homogeneous gasphase a C₃ to C₁₀ ketone with nitrogen dioxide, preferably in thepresence of oxygen and/or water.

DETAILED DESCRIPTION OF INVENTION

A process for selectively forming particular aromatic or aliphatic nitrocompounds comprises contacting in a homogeneous gas phase under elevatedtemperature and pressure reaction conditions, at least one ketone withnitrogen dioxide, preferably in the presence of oxygen and/or water.

The process of homogeneous nitration is generally performed by initiallypreheating the reactants before they are carried into the reaction zone.The preheating conditions are preferably substantially the sametemperature and pressure as the reaction conditions, as fully describedbelow.

The reactant feed of the present process can be selected from aliphaticor aliphatic-aromatic ketone or a mixture thereof. The term "ketone" asused in the present disclosure and in the claims appended hereto refersto compounds having at least one carboxyl oxygen atom covalently bondedto a carbon atom, having from three to ten, preferably three to fivecarbon atoms for aliphatic compounds or seven to ten, preferably sevento eight carbon atoms for aromatic ring containing compounds, and havingthe carbon atom which is bonded to the oxygen be further bonded only tocarbon atoms. The preferred ketones are aliphatic ketones. In view ofnitromethane being the most commercially important product, the mostpreferred compound is acetone.

The particular structure of the oxygenated hydrocarbon used as the feedin the subject process will be the determinative element as to whatnitro compound is to be formed or what predominant nitro compound is tobe formed from a mixture. For example, when the ketone is represented bythe formula: ##STR1## in which R and R' each separately represent analkyl or alkaryl group, when R and R' represents the same alkyl group,one produces RNO₂ as either the sole or dominant nitro product. When thepairs R and R' represent different hydrocarbon groups, the process willform a mixture solely or predominantly of RNO₂ and R'NO₂. These mixturescan be separated by distillation. The preferred ketone are abovecompounds where R and R' are the same hydrocarbon group. The mostpreferred ketone is represented when R and R' are each methyl to therebyform nitromethane as the sole product.

Examples of ketones which are useful as a feed in the subject processare C₃ -C₅ ketones such as acetone, methyl ethyl ketone, diethylketoneand the like. The specific compound will be dictated by the desirednitro compound and the economics and availability of the ketone feedmaterial.

The ketone compounds useful in the present invention preferably do notcontain non-hydrocarbon groups except for the carboxyl oxygen, asdescribed above. However, the compounds may contain non-hydrocarbongroups which will not inhibit the subject process, such as nitriles andthe like. The supply of ketones may also contain small amounts of othercompounds,, such as lower or higher homologs of the ketones describedabove and/or other oxygen atom containg compounds without interferringwith the presently obtained unexpected result.

The above described ketones are contacted in the reaction zone withnitrogen dioxide. The nitrogen dioxide, per se, or precursors (such asN₂ O₄ or HNO₃) capable of forming and providing NO₂ under reaction zoneconditions are feed materials readily obtainable commercially. The terms"nitrogen dioxide", "nitrogen peroxide" or "NO₂ " as used in thisdisclosure and in the appended claims shall each refer to the compoundNO₂ or its precursors except when used to describe the reactant in thereaction zone wherein the terms shall each refer to the compound NO₂,per se.

It is preferred that the feed also includes oxygen, usually in the formof air. The oxygen as well as the nitrogen dioxide can be at leastpartially obtained from recycled unreacted materials which have beenseparated and purified by conventional methods from the reaction productas more fully described below.

The feed may further contain inert gas such as nitrogen, carbonmonoxide, carbon dioxide, argon or mixtures thereof. Further, the feedcan contain water either as part of the carrier for the ketone reactantfeed or as a part of the nitrating agent.

The conditions and parameter ranges for conducting the homogeneousgaseous nitration of an ketones are that the reaction zone feed be in amolar ratio of NO₂ or equivalent to ketone of from about 0.3 to 4 orgreater and preferably from about 0.5 to 3. The environment can be,therefore, either a reducing or an oxidizing environment depending onthe feed ratio used. When oxygen is used as an additional feed, itshould be in from about 0.05 to 1 mole per mole of NO₂ or equivalent.The reaction is carried out at elevated temperature of from about 100°to about 500° C. and preferably from 150° to 400° C. The reaction iscarried out under elevated pressure of from about 5 to 20 bars with from5 to 12 bars being preferred. It has been found that by causing thehomogeneous gaseous nitration to occur under the combined temperatureand high pressure conditions stated herein one attains a high yield ofnitrocompounds with very high selectivity to a specific nitrocompound,e.g. RNO₂, as described above. These achievements are highly desired andattainable only under the present reaction conditions. The combinedtemperature and pressure conditions must be such as to maintain thereactants in a homogeneous gas phase.

The inert gases in the feed (A, CO, CO₂, N₂) can be from about 0 to 90volume percent. The water can be from about 0 to 30 weight percent basedon the NO₂ with at most 10 being preferred. The reaction contact time ofthe reaction gases in the reaction zone can be from about 0.5 to 20seconds with the order of from about 1 to 12 seconds being preferred.

Referring to the drawing to illustrate the subject process, an ketonesuch as acetone, etc. is transported from a reservoir (not shown) bypipeline 1 to preheater 2. Preheater 2 is also used to preheat theketone and, if any, other oxygenated hydrocarbon, being recirculatedthrough pipeline 3, as more fully described hereinbelow. The preheateris maintained at substantially the reaction zone entry temperature ofabout 100° to 500° C. and pressure of from about 5 to 20 bars. Thepreheated ketone feed is then passed through pipeline 4 to reactorintake pipeline 5. The nitrogen dioxide and the oxygen (as air, whenused) are introduced to preheater 8 via pipelines 6 and 7, respectively.The preheater 8 is maintained at temperature and pressure conditionssubstantially the same as that of preheater 2. The mixed preheated NO₂/O₂ gases pass through pipeline 9 to reactor intake pipeline 5 usinggas-gas mixing devices such as spargers, venturis, etc. The preheatedgases are passed through reactor 10 which may be in the form of atubular reactor heated by salt at a temperature of from 100° to 500° C.,preferably from 150° to 400° C. and at a pressure of approximately 5 to20, preferably about 5 to 12 bars. The reactor effluents withdrawnthrough pipeline 11 are cooled to ambient temperature in cooler 12 whichuses super-cooled water to rapidly cool the gases. The cooled reactoreffluents are separated in the separator 13. The liquid effluentseparates into organic liquid phase 14 and aqueous liquid phase 15.

The uncondensed gaseous reaction effluents are removed from theseparator 13 through pipeline 16. The uncondensed gaseous reactioneffluents obtained in the present process are generally a mixture ofcomponents composed predominantly of nitrogen monoxide and inert gases.These effluent gases are distinctly different from those encountered inconventional hydrocarbon gaseous nitration processes where the effluentgases are rich in unreacted hydrocarbons. In such conventionalprocesses, the unreacted hydrocarbons must be separated from the NO(which must be separately treated) and recycled as part of the feed.Such separation is complex and costly. In contrast, the presentuncondensed effluent gases of separator 13 are substantially free ofunreacted ketone and thereby do not require separation. Instead, thesegases can be directly treated at station 17 to re-oxidize the nitrogenoxide to nitrogen dioxide for reuse by, for example, directly injectingoxygen into the gaseous effluent. To prevent build-up of inert gases dueto the recycling of gaseous effluent, a purge stream 18 is maintained.

The condensed organic and aqueous liquid phases 14 and 15, respectively,are removed from separator 13 and sent by pipelines 14' and 15' to anazeotropic distillation column 19. When the nitro compound product has alower density than water (i.e. some C₄ and higher nitro compounds) theorganic and aqueous liquid phases 14 and 15 will be in reversed positionin separator 13 to that shown. In such instances (not shown) line 14'will enter the bottom portion of column 19 and line 15' will enter thetop portion of column 19. Azeotropic distillation column 19 normallyoperates at a pressure of about 1.25 bars or less and at temperaturessufficient to azeotropically distill the nitroalkane or nitroaromaticproducts as well as other compounds having a boiling point lower thanthe nitro products, including any unreacted ketone feed with associativewater. These materials are passed via pipeline 20, condenser 21 andpipeline 22 to distillation column 25. Some of the distillate may berecycled to the azeotropic column 19 by pipeline 23. The majority of thewater and the heavy by-products such as acids and the like are removedas bottom products through pipeline 24. This stream containing heavyby-products may be recycled to reactor 10 via line 3.

The distillation column 25 operates at a pressure of about 1.25 bars orless and at a temperature range sufficient to remove overhead anyunreacted ketone as well as any other oxygenated hydrocarbon by-productsuch as a temperature range of from 30° C. to 95° C. The bottom productof column 25 is removed by pipeline 26 and is composed of a mixture of amajor amount of nitroalkanes or mixture of nitroalkanes or nitroaromaticas is appropriate based on the ketone feed used. In addition there maybe present a small amount of water (from the prior azeotropicdistillation) and trace amounts of oxygenated hydrocarbon by-products.The material removed by pipeline 26 is subsequently chemically treated(not shown) to remove any trace oxygenated contaminants then fed to adehydration column (not shown) and where a mixture of nitrocompounds areproduced to a fractionation column (not shown) to recover pure nitroproducts. The nitro product of the present process is either composed ofa single nitro compound, such as nitromethane or of a mixture of nitrocompounds highly selective with respect to one nitro product which isdependent on the starting ketone feed.

The overhead effluent of column 25 is removed by pipeline 27 throughcondenser 28. Some of the distillate may be recycled to column 25 bypipeline 29. The overhead distillate is made up predominantly of ketoneand other oxygenated hydrocarbons which can be readily recycled viapipeline 30 to preheater 2 as part of the feed.

By utilizing a ketone as the feed material in the subject process it hasbeen unexpectedly found that one can readily form nitroalkane ornitroaromatic compounds, that the nitro compound product will be highlyselective based on the particular ketone used as the feed and that theunreacted ketone can be readily separated and recycled as part of thefeed to further improve the effectiveness and efficiency of the subjectprocess. The subject process provides a means of custom directing theformation of a preselected nitro compound.

The following examples are given for illustrative purposes only and arenot meant to be a limitation on the claims appended hereto. All partsand percentages are by weight unless otherwise indicated.

EXAMPLE I

A series of production runs were conducted using acetone as the feed.Each feed material was preheated to 150° C. at 10 bars. The nitrogendioxide and oxygen (when used) were preheated separately from theacetone and water (when used). The preheated feed materials were thenmixed and reacted in a tubular reactor for a residence time of 8seconds. The reactor effluent was quenched. The nitric oxide, carbonmonoxide and carbon dioxide were removed and the nitric oxide treatedwith oxygen to obtain nitrogen dioxide which was recycled to thereactor. The remaining liquid was distilled to azeotropically remove thenitro compound and low boiling oxygenated hydrocarbon includingunreacted acetone. The azeotropic distillate was further distilled toseparate the nitro compound from the oxygenates. The nitro compound wasnitromethane. No. other nitro compound was detected.

                  TABLE II                                                        ______________________________________                                        Run No            1        2                                                  ______________________________________                                        Temperature (°C.)                                                                        300      350                                                Pressure (atm)    10       10                                                 Feed (mmoles/hr)                                                              Acetone           9579     4216                                               Nitrogen Dioxide  1395     2275                                               Water             1699     0                                                  Oxygen            344      361                                                Nitrogen          1948     3907                                               Moles NO.sub.2 /Acetone                                                                         0.14     0.54                                               Product (mmoles/hr)                                                           Nitromethane      76       112                                                Carbon Monoxide   123      400                                                Carbon Dioxide    376      733                                                Methyl Nitrate    0        0                                                  Methanol          26       66                                                 Acetic Acid       865      816                                                Oxygenated HC     62       30                                                 Nitromethane                                                                  Yield %*          13       9                                                  ______________________________________                                         *Moles of nitromethane/total moles of C.sub.1 compounds produced.        

While the invention has been described in connection with certainpreferred embodiments, it is not intended to limit the invention to theparticular form set forth, but, on the contrary, it is intended to coversuch alternatives, modifications and equivalents as defined by theappended claims.

What is claimed is:
 1. A process for selectively forming nitroalkanescomprising contacting in a reaction zone in a homogeneous gas phase andat an elevated pressure of about 5 to 20 bars, a temperature of fromabout 100° C. to about 500° C. and a time of from 0.5 to 20 seconds, aC₃ -C₁₀ aliphatic ketone with nitrogen dioxide and recovering the formednitroalkane compound.
 2. The process of claim 1 wherein the reactionzone further contains oxygen, water or both.
 3. The process of claim 1wherein the ketones is selected from a C₃ to C₅, aliphatic ketone ormixtures thereof.
 4. The process of claim 2 wherein the ketone isselected from a C₃ to C₅ aliphatic ketone or mixtures thereof.
 5. Theprocess of claim 1 wherein the ketone is represented by the formula:##STR2## wherein R and R' each represent the same alkyl group.
 6. Theprocess of claim 2 wherein the ketone is represent by the formula:##STR3## wherein R and R' each represent the same alkyl group.
 7. Theprocess of claim 5 wherein the ketone is acetone.
 8. The process ofclaim 6 wherein the ketone is acetone.
 9. The process of claim 1 whereinthe process further comprises cooling the reaction zone effluent,separating the resulting liquid phase effluent from the non-condensedgaseous effluent and recovering any ketone and returning at least aportion of said ketone the reaction zone.
 10. The process of claim 2wherein the process further comprises cooling the reaction zoneeffluent, separating the resulting liquid phase effluent from thenon-condensed gaseous effluent and recovering any ketone and returningat least a portion of said ketone to the reaction zone.
 11. The processof claim 3 wherein the process further comprises cooling the reactionzone effluent, separating the resulting liquid phase effluent from thenon-condensed gaseous effluent and recovering any ketone and returningat least a portion of said ketone to the reaction zone.
 12. The processof claim 4 wherein the process further comprises cooling the reactionzone effluent, separating the resulting liquid phase effluent from thenon-condensed gaseous effluent and recovering any ketone and returningat least a portion of said ketone to the reaction zone.
 13. The processof claim 5 wherein the process further comprises cooling the reactionzone effluent, separating the resulting liquid phase effluent from thenon-condensed gaseous effluent and recovering any ketone and returningat least a portion of said ketone to the reaction zone.
 14. The processof claim 6 wherein the process further comprises cooling the reactionzone effluent, separating the resulting liquid phase effluent from thenon-condensed gaseous effluent and recovering any ketone and returningat least a portion of said ketone to the reaction zone.
 15. The processof claim 7 wherein the process further comprises cooling the reactionzone effluent, separating the resulting liquid phase effluent from thenon-condensed gaseous effluent and recovering any ketone and returningat least a portion of said ketone to the reaction zone.
 16. The processof claim 8 wherein the process further comprises cooling the reactionzone effluent, separating the resulting liquid phase effluent from thenon-condensed gaseous effluent and recovering any ketone and returningat least a portion of said ketone to the reaction zone.
 17. The processof claim 2 wherein the reaction zone pressure is from about 5 to 20bars, temperature is from about 180°-400° C., the O₂ to NO₂ molar ratiois from about 0.05 to 1 and the NO₂ to ketone molar ratio is from about0.3 to
 3. 18. The process of claim 3 wherein the reaction zone pressureis from about 5 to 20 bars, temperature is from about 180°-400° C., theO₂ to NO₂ molar ratio is from about 0.05 to 1 and the NO₂ to ketonemolar ratio is from about 0.3 to
 3. 19. The process of claim 4 whereinthe reaction zone pressure is from about 5 to 20 bars, temperature isfrom about 180°-400° C., the O₂ to NO₂ molar ratio is from about 0.05 to1 and the NO₂ to ketone molar ratio is from about 0.3 to
 3. 20. Theprocess of claim 9 wherein the reaction zone pressure is from about 5 to20 bars, temperature is from about 180°-400° C., the O₂ to NO₂ molarratio is from about 0.05 to 1 and the NO₂ to ketone molar ratio is fromabout 0.3 to
 3. 21. The process of claim 10 wherein the reaction zonepressure is from about 5 to 20 bars, temperature is from about 180°-400°C., the O₂ to NO₂ molar ratio is from about 0.05 to 1 and the NO₂ toketone molar ratio is from about 0.3 to
 3. 22. The process of claim 11wherein the reaction zone pressure is from about 5 to 20 bars,temperature is from about 180°-400° C., the O₂ to NO₂ molar ratio isfrom about 0.05 to 1 and the NO₂ to ketone molar ratio is from about 0.3to
 3. 23. The process of claim 12 wherein the reaction zone pressure isfrom about 5 to 20 bars, temperature is from about 180°-400° C., the O₂to NO₂ molar ratio is from about 0.05 to 1 and the NO₂ to ketone molarratio is from about 0.3 to
 3. 24. The process of claim 13 wherein thereaction zone pressure is from about 5 to 20 bars, temperature is fromabout 180°-400° C., the O₂ to NO₂ molar ratio is from about 0.05 to 1and the NO₂ to ketone molar ratio is from about 0.3 to
 3. 25. Theprocess of claim 14 wherein the reaction zone pressure is from about 5to 20 bars, temperature is from about 180°-400° C., the O₂ to NO₂ molarratio is from about 0.05 to 1 and the NO₂ to ketone molar ratio is fromabout 0.3 to
 3. 26. The process of claim 15 wherein the reaction zonepressure is from about 5 to 20 bars, temperature is from about 180°-400°C., the O₂ to NO₂ molar ratio is from about 0.05 to 1 and the NO₂ toketone molar ratio is from about 0.3 to
 3. 27. The process of claim 16wherein the reaction zone pressure is from about 5 to 20 bars,temperature is from about 180°-400° C., the O₂ to NO₂ molar ratio isfrom about 0.05 to 1 and the NO₂ to ketone molar ratio is from about 0.3to 3.